Conventionally, a non-excited operation type electromagnetic brake control device which controls a non-excited operation type electromagnetic brake to make the non-excited operation type electromagnetic brake an engaged state, a disengaged state, or a holding state has been proposed (for example, Patent Document 1). Under the control of a non-excited operation type electromagnetic brake, in the non-excited state in which the brake is set to the engaged state, a movable core is pushed by spring force, and frictional force which is generated between the movable core and a brake disk and between the brake disk and an anti-movable core generates brake torque. Further, in the excited state in which the brake is set to the disengaged state, the movable core is attracted to a fixed core by magnetic attraction force and thus the brake disk becomes a free state and the brake torque disappears. When attracting the movable core to the fixed core to switch the brake to the disengaged state, a large power is necessary, but the power for holding the movable core in the attracted state after attracting the movable core to the fixed core, that is, the power for switching the brake to the holding state after switching the brake to the disengaged state, may be less than the power which is required when disengaging the brake.
FIG. 6 is a circuit diagram of a conventional non-excited operation type electromagnetic brake control device. The non-excited operation type electromagnetic brake control device 1 shown in FIG. 6 has an AC power supply 2, a brake coil 3, a triangle voltage wave generation unit 4, a comparative voltage wave generation unit 5, a comparison unit 6, switches 7, 8, a control power supply unit 9, and diodes 10, 11.
The brake coil 3 generates a magnetic attraction force by supplying current I from the AC power supply 2 when the switch 8 is turned on due to an instruction from the outside, and switches the non-excited operation type electromagnetic brake (not shown) from the engaged state to the disengaged state. At this time, the current I flows from the brake coil 3 to the anode side of the diode 11. Further, at the same time as when the switch 8 is turned on, a timer (38) starts a measurement. The elapse of a predetermined time after the switch 8 is turned on is measured by the timer (38). When a certain time elapses, the non-excited operation type electromagnetic brake (not shown) is switched from the disengaged state to the holding state.
The triangle voltage wave generation circuit 4 generates a triangle voltage wave comprised of valley parts and peak parts, each of which has the same angle as an angle of each of the valley parts, arranged alternately. For this reason, the triangle voltage wave generation circuit 4, as shown in FIG. 7, has a comparator 21, a CR part 22 which is connected to a non-inverted input part of the comparator 21, a resistance part 23 which is connected to an input part of the triangle voltage wave generation circuit 4, and a resistance 24 with one end which is connected to an output part of the triangle voltage wave generation circuit 4 and an inverted input part of the comparator 21 and with the other end which is connected to an output side of the comparator 21 and the resistance part 23.
The CR part 22 has a resistance 25 with one end which is connected to the non-inverted input side of the comparator 21 and with the other end which is grounded, a capacitor 26 which is connected in parallel to the resistance 25, and a capacitor 27 with one end which is connected to the inverted input side of the comparator 21 and with the other end which is connected to the other end of the resistance 25. The resistance part 23 has a resistance 28 with one end which is connected to the input part of the triangle voltage wave generation circuit 4 and with the other end which is connected to the non-inverted input side of the comparator 21, a resistance 29 with one end which is connected to the input part of the triangle voltage wave generation circuit 4 and with the other end which is connected to the output side of the comparator 21, and a resistance 30 with one end which is connected to the other end of the resistance 28 and with the other end which is connected to the other end of the resistance 29.
When the capacitor 27 is not charged, the potential of the non-inverted input side of the comparator 21 is higher than the potential of the inverted input side of the comparator 21, so the output of the comparator 21 becomes high. On the other hand, when the capacitor 27 is charged and the potential of the inverted input side of the comparator 21 exceeds the potential of the non-inverted input side of the comparator 21, the output of the comparator 21 becomes low. The charging/discharging time of the capacitor 27 is determined by the CR value of the CR part 22 and the resistance value of the resistance part 23.
The comparative voltage wave generation unit 5 generates a comparative voltage wave based on the current I. For this reason, the comparative voltage wave generation unit 5 has a shunt resistance 31 which detects the current I and converts the detected current I to voltage to generate the comparative voltage wave.
The comparison unit 6 compares the triangle voltage wave value with the comparative voltage wave value when the non-excited operation type electromagnetic brake (not shown) is in the holding state. For this reason, the comparison unit 6 has a comparator 32 and a switching part 33 comprised of an npn type transistor whose gate is connected to the output side of the comparator 32 and a pnp transistor whose gate is connected to the output side of the comparator 32.
The switch 7 as a switching unit performs switching to supply current I to the brake coil 3 when the triangle voltage wave value is larger than the comparative voltage wave value and to cut off the supply of current I to the brake coil 3 when the triangle voltage wave value is not lager than the comparative voltage wave value, and reduces the average current which flows through the brake coil 3 when the non-excited operation type electromagnetic brake (not shown) is in the holding state. For this reason, the switch 7 is comprised of IGBT (insulated gate bipolar transistors), Darlington transistors, thyristors, Triac's®, or other semiconductor devices.
The control power supply unit 9 supplies power for starting up the comparator 32, turning the switch 7 on/off, etc. For this reason, the control power supply unit 9 has a control power supply 34, a rectifier unit 35 which is comprised of four diodes, a resistance 36 which is connected between one end of the control power supply 34 and one end of the rectifier unit 35, and a transformer 37 which is connected to the rectifier unit 35.
FIG. 8 is a graph which shows time change of current which flows through a brake coil of the non-excited operation type electromagnetic brake control device of FIG. 6. During the time t1 when the non-excited operation type electromagnetic brake (not shown) is in the disengaged state, the brake coil 3 is continuously supplied with current I1 from the AC power supply 2. As opposed to this, during the time t2 when the non-excited operation type electromagnetic brake (not shown) is in the holding state, as explained later, the switch 7 is used to switch between the continuation of the supply of the current to the brake coil 3 and the cutoff of the supply of the current to the brake coil 3 every carrier period of the triangle voltage wave. Therefore, the average current I2 which flows through the brake coil during the time t2 is smaller than the current I1 which flows through the brake coil during the time t1.
FIG. 9 is a graph which shows time change of the triangle voltage wave and the comparative voltage wave which are generated in the non-excited operation type electromagnetic brake control device of FIG. 6. While the non-excited operation type electromagnetic brake (not shown) is in the disengaged state, the capacitors 26, 27 of the triangle voltage wave generation unit 4 are charged and control voltage is generated by the control power supply unit 9 for raising the comparative voltage wave. On the other hand, when the non-excited operation type electromagnetic brake (not shown) is in the holding state, the control voltage from the control power supply unit 9 falls, the comparative voltage wave is lowered, and the comparison unit 6 compares the comparative voltage wave with the triangle voltage wave. During the time ONduty when the triangle voltage wave is higher than the comparative voltage wave in one carrier period T of the triangle voltage wave, the transistor 7 is turned on, while during the time OFFduty when the triangle voltage wave is not higher than the comparative voltage wave in one carrier period T of the triangle voltage wave, the transistor 7 is turned off.
In this way, in the holding state of the non-excited operation type electromagnetic brake, when the triangle voltage wave value is larger than the comparative voltage wave value, the switch 7 is turned on and current I is supplied to the brake coil 3, on the other hand, when the triangle voltage wave value is not longer than the comparative voltage wave value, the switch 7 is turned off and the supply of current I to the brake coil 3 is cut off to thereby reduce the average current which flows through the brake coil 3.